An electrophotographic image forming apparatus uses a belt unit to transport a recording sheet. The belt unit is provided to oppose a photosensitive drum, wherein a toner image is transferred from the photosensitive drum to the recording sheet transported by the belt unit. In addition, when an intermediate transfer belt is used in a belt unit temporarily holding the toner image to be formed on the recording sheet, the belt unit is also provided to oppose a photosensitive drum.
Then, these belt units have to be accurately positioned with respect to an apparatus body in order to form a toner image at an accurate position with respect to a recording sheet and, in case of color printing, in order to prevent occurrence of color shift. For example, in an image forming apparatus, the position of the belt in its moving direction is defined by pressing the bearing of a roller, around which the belt is looped, against a positioning section of a frame.
However, in the image forming apparatus, due to the setting of the operating timing or the peripheral speed of the belt or the photosensitive drum, a force acts to move the belt from the photosensitive drum toward the belt unit. In this image forming apparatus, since this force acts in a direction of separating the bearing of the belt unit away from the positioning section, there is a possibility that the position of the belt in the moving direction of the belt would become unstable.